Abstract
The release mechanism of the rat atrial granules containing atrial natriuretic polypeptide (ANP) was examined. In addition, the ultrastructure of right atrial myocardiocytes incubated in a medium containing an excess calcium and calcium ionophores (A 23187) was investigated by electron microscopy. After 3-15 minute incubation in the medium, many ANP-containing atrial specific granules were detected in the vicinity of the subsarcolemmal region, and invagination of the plasma membranes occurred as well as a large number of vacuoles were observed. After incubation with an excess calcium and calcium ionophores for 40 minutes, the atrial specific granules had completely disappeared and numerous vacuoles appeared in the sarcoplasm of the atrial myocardiocytes. Thus, release of ANP and their reabsorption by membranes were accelerated by the presence of calcium and calcium ionophores.
